From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8A56DC43331 for ; Tue, 19 Jan 2021 18:28:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 44A5922CAD for ; Tue, 19 Jan 2021 18:28:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388983AbhASQoi (ORCPT ); Tue, 19 Jan 2021 11:44:38 -0500 Received: from foss.arm.com ([217.140.110.172]:39494 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389388AbhASQlR (ORCPT ); Tue, 19 Jan 2021 11:41:17 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8B736D6E; Tue, 19 Jan 2021 08:40:31 -0800 (PST) Received: from e107158-lin (e107158-lin.cambridge.arm.com [10.1.194.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 754583F66E; Tue, 19 Jan 2021 08:40:30 -0800 (PST) Date: Tue, 19 Jan 2021 16:40:27 +0000 From: Qais Yousef To: Quentin Perret Cc: "Peter Zijlstra (Intel)" , Dietmar Eggemann , Vincent Guittot , linux-kernel@vger.kernel.org, Valentin Schneider , Morten Rasmussen Subject: Re: [PATCH] sched/eas: Don't update misfit status if the task is pinned Message-ID: <20210119164027.drfpmrol3xhf4ckc@e107158-lin> References: <20210119120755.2425264-1-qais.yousef@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/19/21 15:35, Quentin Perret wrote: > On Tuesday 19 Jan 2021 at 12:07:55 (+0000), Qais Yousef wrote: > > If the task is pinned to a cpu, setting the misfit status means that > > we'll unnecessarily continuously attempt to migrate the task but fail. > > > > This continuous failure will cause the balance_interval to increase to > > a high value, and eventually cause unnecessary significant delays in > > balancing the system when real imbalance happens. > > > > Caught while testing uclamp where rt-app calibration loop was pinned to > > cpu 0, shortly after which we spawn another task with high util_clamp > > value. The task was failing to migrate after over 40ms of runtime due to > > balance_interval unnecessary expanded to a very high value from the > > calibration loop. > > > > Not done here, but it could be useful to extend the check for pinning to > > verify that the affinity of the task has a cpu that fits. We could end > > up in a similar situation otherwise. > > Do you mean failing the sched_setaffinity syscall if e.g. the task > has a min clamp that is higher than the capacity of the CPUs to which it > will be pinned? If so, I'm not sure if we really want that. No. In Android for instance, I'm worried a background task affined to little cores that has a utilization > capacity_of(little) will trigger the same problem. It'll be affined to more than just 1 cpu, but none of the little cpus will actually fit. Makes sense? > But this patch makes sense on its own for sure, so: > > Reviewed-by: Quentin Perret Thanks -- Qais Yousef